US service awards five study contracts for transformational requirement, but is programme ambitious enough?

Super-heavylift aircraft designs picked by a US military panel to compete for what could be one of the most ambitious rotorcraft projects in history have stirred strong debate about the technical boldness of the five candidates.

On one hand, each of the five selected design concepts promise in different ways to revolutionise payload capabilities for vertical take-off and landing (VTOL) aircraft. The US Army’s Applied Aviation Technology Directorate (AATD) is seeking a new Joint Heavy Lift (JHL) aircraft that can lift a Stryker-class vehicle more than 460km (250nm), which exceeds the payload limits of conventional rotorcraft by at least a factor of two.

Chinook  US Army Big

However, each of the proposals selected by the AATD team last month for an 18-month concept definition phase is also familiar. Each is a scaled-up version of a rotorcraft design rooted in a well-tested configuration.

Boeing’s tandem rotor offering, for example, is an updated and enlarged version of the all-composite Model 360 prototype that it tested and abandoned in the late 1980s. That model was based on the design of the 1960s-era Boeing CH-46 Sea Knight. Sikorsky’s two selected coaxial rotor designs also stem from a cancelled project in the 1980s.

Bell Boeing’s quad-tiltrotor proposal and the optimum-speed tiltrotor design submitted by Karem – formerly Frontier Aircraft – also represent new and more complex applications of legacy technology. Other potentially disruptive – but virtually untested – concepts known to have been submitted to the AATD panel were excluded from the last round. Those included configurations such as monotiltrotor, a giant gyrocopter and a high-speed compound helicopter.

Bruce Tenney, an AATD official leading the JHL concept definition phase, says the army received 14 proposals. Asked if he was satisfied by the quality of the submissions, he initially paused, then replied: “No comment.” However, Tenney adds that he is pleased with the mix and quality of the five selected designs, but notes without elaboration that there are “a couple” of desired concepts that had not been submitted.

Abe Karem, founder of Karem and a pioneer of optimum-speed rotor design, has strongly defended the innovative qualities of not only his proposed solution, but also his fellow competitors in the JHL concept-definition stage.

Neither the Boeing tandem rotor, Sikorsky coaxial rotor nor Bell Boeing quad-tiltrotor represent merely “warmed-up” versions of old technology, he says. Although Tenney refers to the Boeing tandem rotor as the least complex option among the five proposals, Karem believes Boeing’s concept is much more sophisticated than it appears on the surface.

One of the losing bidders, however, thinks the AATD unfairly ruled out the most truly innovative designs. Jay Carter, founder of CarterCopter, submitted a proposal for a Pratt & Whitney F135-powered compound helicopter. It would be capable, in theory, of VTOL-like performance while carrying a Stryker-class vehicle more than 1,600km and travelling at 350kt (640km/h).

Carter says the AATD explained his proposal was rejected for being “non-responsive” on a number of points, such as for not providing specific fuel consumption rates for the F135 and estimating future manufacturing costs.

However, Carter says, CarterCopter has no access to F135 performance data because it is not already a defence contractor. The company also is not a manufacturer, he adds, and is unable to accurately estimate production costs. “To be competitive, we would have to team with a major aerospace company,” Carter says. “But none of the big aerospace companies want to team with us until they know the military is interested in the technology.”

The USA formally launched the JHL concept definition phase 12 months ago. Michael Wynne, then-undersecretary for acquisition, technology and logistics, directed the army to lead a three-year effort to analyse the technical feasibility and operational requirements for such an aircraft.

The American Helicopter Society (AHS) completed a study two years ago which determined that the project would require a huge investment in basic research over five to six years before full-scale development could begin. JHL requires fundamental advances in lightweight, high load-bearing materials and propulsion capability, the AHS says.

Boeing, however, rejects the study’s conclusions, saying that its tandem rotor proposal is based on relatively mature technologies and can be developed and fielded within a total of eight years.

Meanwhile, the army is seeking to attract greater participation from the US Navy and US Air Force by the end of the current-concept definition phase. The navy has chipped in $1 million for the study effort, but the balance of the $30 million funding is paid for by the army alone. The USAF is participating in the concept studies, but has not contributed funds to the initiative.

Separately, the US Marine Corps has been cleared to resume work on its Heavy Lift Rotorcraft programme, a $4 billion effort that seeks to develop a more powerful version of its current Sikorsky CH-53D Super Stallion. Programme funds were frozen early this year after cost estimates jumped by around $600 million.

This budget increase has now been accepted by the USN, however, and Sikorsky is now preparing to launch a long-delayed competition to select the aircraft’s engine.


Source: Flight International